1. Field of the Invention
The present invention relates to improved release agent compositions, such as mold release agents or parting agents, and processes in which such agents are applied to one surface, such as mold surface or backing surface, to enable or facilitate the release or separation of the surface of a molded or formed body, such as of cured or solidified molding resin or elastomer, from the mold surface or backing surface without damage to either surface.
A preferred embodiment of the present invention relates to the filling of gaps between aircraft bulkheads and inlet duct surface skins of composite materials, which skins must be removed to inspect for voids in the cured gap-fill or shim layer and for the application of sealant before the composite skins and bulkhead as reassembled.
2. State of the Art
A wide variety of mold release agents are known in the art, most of which are solid additives to resinous molding compositions which melt and exude to the surface of the molded body to facilitate release from the surface of the mold after the molding cycle.
It is also known to apply volatile organic solvent solutions or aqueous dispersions or emulsions of release agent composition to mold surfaces or backing surfaces prior to the curing of resinous shim or gap-fill compositions, such as polyurethane foam compositions, or ceramic compositions thereagainst and reference is made to U.S. Pat. Nos. 4,609,511 and 5,133,804 respectively, for their disclosure of such processes and mold release compositions.
The use of mold release compositions containing major amounts of volatile vehicles is objectionable because of the internal pressures caused by the evaporation of the vehicle, the formation of voids in the molded body and the dangers introduced in the case of volatile organic vehicles.
The conventional method for shimming or filling the gaps between composite inlet duct surface skins and aircraft bulkheads involves applying Teflon .RTM. polytetrafluoro-ethylene film or tape to the bulkhead surface, coating the film or tape with a spray wax release agent, applying thereover a layer of liquid curable shim or gap-fill composition such as a curable silicone elastomeric caulk layer, and applying thereover a conforming composite skin section such as an inlet duct section. In order to force and distribute the liquid shim material into the gap between the composite skin and the bulkhead, a conventional clamping fixture with an inflatable bladder is installed over the skin and inflated to compress the skin against the bulkhead and distribute the liquid shim, as needed, to fill the gap. Then the liquid shim composition is cured, such as by application of heat, to solidify the shim material. After cooling, the bladder tool and composite skin section can be separated from the bulkhead to inspect for voids in the cured shim layer.
The major disadvantage of the conventional process and release agents is the unsatisfactory release provided by the Teflon .RTM./wax, sometimes resulting in damage and delamination of the composite skin when the cured shim material does not release completely from the bulkhead. Also, the Teflon.RTM./wax requires two-step application, and is difficult to remove from the surface of the cured shim layer.
Conventional release agents and lubricating agents contain waxes and fatty acids, oils such as vegetable and/or mineral axes and oils and/or normally solid lubricants such as petrolatum waxes, aliphatic alcohols, including cetyl alcohol, and a wide variety of mixtures of such materials, as disclosed by U.S. Pat. Nos. 4,609,511 4,035,514 and 4,808,323. Such compositions are unsatisfactory for a variety of reasons including complexity of formulations, presence of liquid vehicles such as water or volatile organic solvents, and other properties such as fluidity which render the compositions difficult or messy to apply uniformly by brushing or wiping and/or which do not provide satisfactory release properties to permit complete release of a composite body from a cured shim material without any delamination.